Treatment of unresectable locally advanced non-small cell lung cancer includes radiotherapy which is limited by its toxicity to normal lung, particularly when treating larger-volume disease. We shall investigate a complementary biological approach to lower radiation toxicity in the normal lung included in the treatment plan, and yet increase radiation effect in the tumor target, using soy isoflavones. Mixtures of natural soy isoflavones containing genistein, daidzein and glycitein can sensitize cancer cells to ionizing radiation by inhibiting pathways of cell survival which are constitutively activated in cancer cells and not in normal cells, and are upregulated further by radiation. Soy isoflavones can also act as anti-oxidants in normal tissues thus protecting them from radiation-induced toxicity. We therefore propose that soy isoflavones could give a similar protection to irradiated normal lung, and at the same time, enhance cell killing in the tumor volume during radiotherapy, thus further improving the therapeutic effect of standard-of-care radiotherapy. The proposed studies are supported by our preliminary data demonstrating enhanced antitumor effect of radiation in human A549 xenograft lung tumor nodules in mice, and simultaneous radioprotection of the normal lung tissue by soy isoflavones. Our specific aims are first to define the combinations of radiation dose, soy concentration and duration of soy exposure, which result in decreased survival of carcinoma cells and increased survival of normal cells using in vitro models. Then, to fully evaluate this combined modality approach in vivo, in human lung tumors growing in the lungs of nude mice, hypothesizing enhancement of effect, and to monitor changes in normal lung tissue, expecting protection against radiation damage by soy isoflavones. To achieve these aims in vitro, we shall measure cell survival by clonogenic assay, DNA damage by the 3-H2AX immunofluorescence assay and modulation of molecular pathways involved in the interaction between radiation and soy isoflavones, including APE1/Ref-1, NF-:B, HIF-11. To achieve our aims in vivo, we shall determine anti-tumor response by enumeration of lung nodules, morphometric measurements of lung sections, and by immunohistochemistry with Ki-67 proliferation marker and TUNEL assay for apoptosis as well as the use of non-invasive luminescence imaging. The effect of combining radiation with soy isoflavones in normal lung tissue, will be assessed by monitoring mouse survival and weight, DNA damage, inflammation and inflammatory cytokines, fibrosis and oxidative damage. The results of this investigation will have high impact on the management of patients diagnosed with lung cancer.